FIG. 12 is a perspective view of a semiconductor laser device including a semiconductor laser chip 1 that is disposed on an electrically insulating heat sink 2, such as SiC, which, in turn, is mounted on a block 3 of a good thermal conductor, such as silver or a copper/tungsten alloy. An electrode 4' extends from the interface of the semiconductor laser chip 1 and the heat sink 2 and is electrically connected to the block 3 by a wire 5. A surface electrode 4 on the opposite surface of the semiconductor laser chip 1 from the heat sink 2 is connected by a wire 6 to one terminal 7 of a power supply (not shown). The block 3 is electrically connected to the other terminal of the power supply.
FIG. 13 is a schematic diagram of a conventional semiconductor laser device circuit including a laser diode LD, such as the semiconductor laser device shown in FIG. 12, and a driver V. The driver V produces a large current pulse that is supplied to the semiconductor laser LD. The circuit of FIG. 13 includes a reverse current blocking diode D connected in parallel to and in the same polarity as the power supply. The reverse current blocking diode D and driver V are connected through a parasitic inductance L to the laser diode LD. The parasitic inductance L is an inherent feature of the circuit and is not an added inductance. When the driver V produces a forward-going pulse for the laser diode LD, the parasitic inductance L may cause a counter electromotive force (emf) to be produced with a magnitude v=-L*dI/dt where L is the inductance of the parasitic inductance and dI/dt is the rate of change of the current through the circuit with time. The reverse polarity counter emf produces a current that is blocked by the reverse current blocking diode D, thereby protecting the driver V. However, if the magnitude of the counter emf exceeds the maximum reverse bias voltage that the laser diode LD can withstand, then a large reverse current flows in the laser diode LD. This large reverse current can damage and even destroy the laser diode LD.